This invention relates to new ethylene-based polymer compositions formed by high pressure processes in the presence of a molecular catalyst and a free radical initiator. In conventional polymerizations of ethylene-based polymers, catalysts, such as metallocene catalysts, post-metallocene catalysts and Ziegler-Natta catalysts, when used in a high pressure reactor, result in excessive reactor fouling. In addition, such catalysts, under high pressures, are highly susceptibility to decompositions, and form high molecular weight polymers and gels. These catalysts are also deactivated by polar impurities in the reactor. In a commercial production plant with an ethylene recycle system, polar impurities can be produced from either the breakdown products from the free radical initiator or from agents used for catalyst deactivation. Thus, there is a need for polymerization processes to form new ethylene-based polymer compositions, and which do not result in reactor fouling. There is a further need for such processes that form lower amounts of decomposition products and lower amounts of high molecular weight polymer and gels.
GB 1205635 discloses the continuous polymerization of ethylene in two or more zones, comprises passing ethylene through a first polymerization zone, at a pressure of not less than 1600 atmospheres and a temperature of not less than 125° C., in the presence of a Ziegler type initiator; and passing the mixture of polymer and unreacted monomer to a second zone, at a pressure of at least 1600 atmospheres, and a temperature higher than the lowest temperature in the first zone, and in the presence of a free-radical initiator.
International Publication No. WO 2010/141557 discloses a process for polymerizing ethylene, in the presence of a catalyst, to form a crystalline ethylene-based polymer, having a crystallinity of at least 50%, in a first reactor or a first part of a multi-part reactor. The crystalline ethylene-based polymer is reacted with additional ethylene, in the presence of a free-radical initiator, to form an ethylenic polymer, in at least one other reactor or a later part of a multi-part reactor.
International Publication No. WO 2009/114661 discloses an ethylenic polymer comprising amyl groups (about 0.1 to about 2.0 units per 1000 carbon atoms), and a peak melting temperature, Tm, in ° C., and a heat of fusion, Hf, in J/g. The numerical values of Tm and Hf correspond to the relationship Tm >(0.2143*Hf)+79.643.
Additional polymerizations and/or polymers are disclosed in the following references: U.S. Pat. Nos. 5,084,534, 5,753,578; International Publication Nos. WO 2007/136494, WO 2011/032172; Rau et al., Kinetic Investigations of the Metallocene-Catalyzed Polymerization of Ethylene at High Pressure, Chem. Eng. Technol. 25, 2002, 5, 494-498; Götz et al., Influence of Aluminum Alkyl Compounds on the High-Pressure Polymerization of Ethylene with Ternary Metallocene-Based Catalysts. Investigation of Chain Transfer to Aluminum, Macromolecular Materials and Engineering, 2002, 287, 16-22; Luft et al., and High Pressure Polymerization of Ethylene with a Homogeneous Metallocene Catalyst, Die Angewandte Makromolekulare Chemie, 212, 1993, 157-166.
As discussed above, there remains a need for polymerization processes to form new ethylene-based polymer compositions, and which do not result in reactor fouling. There is also a need for such processes that do not result in injector plugging. There is a further need for such processes that form lower amounts of decomposition products and lower amounts of high molecular weight polymer and gels; and there is a need to form polymers with excellent processibility. These needs have been met by the following invention.